1. Field of the Invention
The present invention pertains to a method and apparatus for treating congestive heart disease and related valvular dysfunction. More particularly, the present invention is directed to a measurement device for determining an appropriate size for a cardiac reinforcement device for a particular heart.
2. Description of the Prior Art
Congestive heart disease is a progressive and debilitating illness. The disease is characterized by a progressive enlargement of the heart.
As the heart enlarges, it is forced to perform an increasing amount of work in order to pump blood in each heart beat. In time, the heart becomes so enlarged the heart cannot adequately supply blood. An afflicted patient is fatigued, unable to perform even mildly exerting tasks and experiences pain and discomfort. Further, as the heart enlarges, the internal heart valves may not adequately close. This impairs the function of the valves and further reduces the heart""s ability to supply blood.
Congestive heart failure has an enormous societal impact. In the United States alone, about five million people suffer from the disease (Classes I through IV combined). Alarmingly, congestive heart failure is one of the most rapidly accelerating diseases (about 400,000 new patients are diagnosed in the United States each year). Economic costs of the disease have been estimated at $38 billion annually.
Not surprisingly, substantial effort has been made to find alternative treatments for congestive heart disease. Recently, a new surgical procedure has been developed. Referred to as the Batista procedure, the surgical technique includes dissecting and removing portions of the heart in order to reduce heart volume. This is a radical, new, experimental procedure that is subject to substantial controversy. Furthermore, the procedure is highly invasive, risky and expensive and commonly includes other expensive procedures (such as a concurrent heart valve replacement).
Cardiomyoplasty is a recently developed treatment for earlier stage congestive heart disease. In this procedure, the latissimus dorsi muscle (taken from the patient""s shoulder) is wrapped around the heart and chronically paced synchronously with ventricular systole. Pacing of the muscle results in muscle contraction to assist the contraction of the heart during systole.
Even though cardiomyoplasty has demonstrated symptomatic improvement, studies suggest the procedure only minimally improves cardiac performance. The procedure is highly invasive requiring harvesting a patient""s muscle and an open chest approach (i.e., sternotomy) to access the heart. Furthermore, the procedure is expensive, especially when a paced muscle is utilized, because a costly pacemaker is required. The cardiomyoplasty procedure is complicated. For example, it is difficult to adequately wrap the muscle around the heart and attain a satisfactory fit. Also, if adequate blood flow is not maintained to the wrapped muscle, the muscle may necrose. The muscle may stretch after wrapping, reducing its constraining benefits, and the muscle is generally not susceptible to post-operative adjustment. Finally, the muscle may fibrose and adhere to the heart causing undesirable constraint on the contraction of the heart during systole.
While cardiomyoplasty has resulted in symptomatic improvement, the nature of the improvement is not understood. For example, one study has suggested the benefits of cardiomyoplasty are derived less from active systolic assist than from remodeling, perhaps because of an external elastic constraint. The study suggests an elastic constraint (i.e., a non-stimulated muscle wrap or an artificial elastic sock placed around the heart) could provide similar benefits. Kass et al., Reverse Remodeling From Cardiomyoplasty In Human Heart Failure: External Constraint Versus Active Assist, 91 Circulation 2314-2318 (1995). Similarly, cardiac binding is described in Oh et al., The Effects of Prosthetic Cardiac Binding and Adynamic Cardiomyoplasty in a Model of Dilated Cardiomyopathy, 116 J. Thorac. Cardiovasc. Surg. 148-153 (1998), Vaynblat et al., Cardiac Binding in Experimental Heart Failure, 64 Ann. Thorac. Surg. 81-85 (1997) and Capouya et al., Girdling Effect of Nonstimulated Cardiomyoplasty on Left Ventricular Function, 56 Ann. Thorac. Surg. 867-871 (1993).
In addition to cardiomyoplasty, mechanical assist devices have been developed as intermediate procedures for treating congestive heart disease. Such devices include left ventricular assist devices (xe2x80x9cLVADxe2x80x9d) and total artificial hearts (xe2x80x9cTAHxe2x80x9d). An LVAD includes a mechanical pump for urging blood flow from the left ventricle into the aorta. Such surgeries and devices are expensive. The devices are at risk of mechanical failure and frequently require external power supplies. TAH devices are used as temporary measures while a patient awaits a donor heart for transplant.
Commonly assigned U.S. Pat. No. 5,702,343 to Alferness dated Dec. 30, 1997 teaches a jacket to constrain cardiac expansion during diastole. Also, PCT International Publication No. WO 98/29401 published Jul. 9, 1998 teaches a cardiac constraint in the form of surfaces on opposite sides of the heart with the surfaces joined together by a cable through the heart or by an external constraint. U.S. Pat. No. 5,800,528 dated Sep. 1, 1998 teaches a passive girdle to surround a heart. German utility model DE 295 17 393 describes a non-expansible heart pouch. PCT International Publication No. WO 98/58598 published Dec. 30, 1998 describes a cardiac pouch with an elastic limit.